Method for processing of red mud

ABSTRACT

The red mud by-product of aluminum manufacture is processed by first removing its alkali metal content by causticization of a slurry thereof with burnt lime in the presence of humic acid or derivative thereof. From the remaining solids iron can be recovered such as by reduction and smelting, where the humic acid-containing ingredient, a soft coal, can be utilized for its carbon content. From the remaining slag of the smelting either an aluminaceous refractory cement is prepared or the solids are converted into a spontaneously disintegrating dicalcium silicate from which the aluminum content can be recovered. In the latter case the last remaining solids can be used in the manufacture of portland cement.

United States Patent [191 Kapolyi et a1.

Dec. 4, 1973 METHOD FOR PROCESSING OF RED MUD [73] Assignee: TatabanyaiSzenbanyak, Tatabanya,

Hungary Filed: Dec. 2, 1971 Appl. No.2v 204,216

[30] Foreign Application Priority Data Dec. 4, 1970 Hungary TA-1907 [56]References Cited UNITED STATES PATENTS 2,981,600 4/1961 Porter 423/1212,438,488 3/1948 Anderson et al. 106/100 X OTHER PUBLICATIONS Miller eta1. Chem. Abstracts, 54 13573f, 1960.

Watanabe, Chem. Abstracts, 55 P879f, 1960.

Encyclopedia of Chem. Tech. Kirk-Othmer, V01. 4, 2nd Ed. TP9E68; 1964,(Pp. 694-695 Slag Cements relied on).

Primary ExaminerL. Dewayne Rutledge Assistant Examiner-M J. AndrewsAttorney-Gabriel P. Katona [57] ABSTRACT The red mud by-product ofaluminum manufacture is processed by first removing its alkali metalcontent by causticization of a slurry thereof with burnt lime in thepresence of humic acid or derivative thereof. From the remaining solidsiron can be recovered such as by reduction and smelting, where the humicacidcontaining ingredient, a soft coal, can be utilized for its carboncontent. From the remaining slag of the smelting either an aluminaceousrefractory cement is prepared or the solids are converted into aspontaneously disintegrating dicalcium silicate for which the aluminumcontent can be recovered. In the latter case the last remaining solidscan be used in the manufacture of portland cement.

9 Claims, 1 Drawing Figure 1? T L PM 41,

7;? 1 Le 21 x25 1 METHOD FOR PROCESSING OF RED MUD The present inventionrelates to a process for the treatment of red mud obtained in theproduction of aluminum. More particularly, the process of the presentinvention relates to the reduction of the chemically combined alkalimetal in the red mud, for recovery of its iron and aluminum content andfor utilization of the remainder in the manufacture of cement.

Red mud is a heretofore useless by-product of bauxite processing. Thismaterial is usually collected in large, space-consuming waste piles inthe vicinity of aluminum-manufacturing plants. Since red mud cantypically contain 35 50 percent ferric oxide and 6 10 percent sodiumoxide, solids basis, it could provide a desirable source of raw materialeven for the recovery of thesodium alone. After the removal of thesodium content other valuable ingredients can also be recovered, becausethe presence of sodium prevents the recovery of the other components.

Prior art efforts for the economical utilization of alkalimetal-containing red mud included a reduction thereof, followed bysmelting. The resulting steel was of a poor grade, and its high sodiumcontent prevented the utilization of the slag remaining after thesmelting. Furthermore, the sodium vapors which formed during thesmelting, penetrate the interstices of the firebricks in the smeltingfurnaces, resulting in a high degree of refractory corrosion andpremature destruction of the kilns.

Hence, the condition for economical, large, industrial scale utilizationof red mud is the separation of the alkali metal components to permitrecovery of possibly all of its other components. It is known partiallyto recover sodium oxide from red mud by treatment with caustic lime toobtain sodium hydroxide. In this proce dure the red mud by-product ofthe Bayer bauxite process is slurried with 6 l2 percent burnt lime, andwhen heated to 85 100 C even after a period of 4 8 hours reaction timeonly a l 25 percent recovery can be obtained. As the lime concentrationis increased the recovery of sodium hydroxide increases only to a pointbeyond which no increase in the recovery will occur. This is because thesodium lime reaction is reversible and as sodium hydroxide is formed itsuppresses the completion of the reaction. This means that after thecaustic treatment the red mud still contains appreciable amounts 3 7percent of sodium oxide in the form of sodalite or other chemicalcombinations. On the other hand, economical treatment of red mud wouldrequire that the alkali metal content should be under 1.5 percent. Thiscannot be accomplished with prior art techniques.

' it is an object of the invention to recover the alkali metalscontained in red mud by reducing the alkali metal concentration to avalue below 1.5 1 percent by weight of solids, recovering the ironcontent of the thus obtained alkali-poor material and then utilising theiron-and alkali-poor material for directly manufacturing high aluminarefractory cements or to obtain a material of high dicalcium silicatecontent which will spontaneously disintegrate and from which aluminumcan be leached out and, finally, the remainder can be used for themanufacturing of portland cement. Also valuable fertilizer materials canbe obtained from byproducts of the process of the present invention.

In accordance with the invention a mixture of red mud, burnt lime andhumic acid and/or derivatives of humic acid is slurried in an aqueousmedium. The suspension is intensively agitated between about and about Cfor a period of from about 1 to about 6 hours. By that time a largeproportion of the alkali metals of the red mud goes into solution asalkali humates which can either be directly utilised or converted foruse into hydroxides or carbonates. Then the remainder is subjected toreduction and smelting to recover its iron content. Thereafter a clinkeris formed from the remaining material, while optionally adjusting itscalcium content to desirable levels, so that the resulting dicalciumsilicate, upon cooling, will spontaneously disintegrate to permit easyextraction of the aluminate content thereof. The remainder can befinally utilised for the production of portland cement.

The present invention is based on the recognition that humic acidspromote the causticisation of red mud, because the physicallyinseparable, chemically bound sodium ions liberated duringcausticisation, will form poorly dissociating water soluble humates.Thus the reaction equilibrum is shifted in a desirable direction whichenables a more complete removal of the sodium oxide and its conversionto various humic acid derivatives.

Suitably brown coals such as lignites can be used as the humicacid-containing ingredient. These not only provide the humic acid neededfor forming its sodium derivatives, but will also furnish the carbonneeded for the reduction of the iron content of the red mud. Other softcoal varieties such as peat coal, which contain humic acid as well ascarbon, can also be used in accordance with this feature of the presentinvention.

The process is described below in greater detail, with reference to theschematic drawing which is an illustration of a preferred embodiment ofthe invention.

Burnt lime (l) and a coal containing humic acid or a humic acidderivative (2) are ground and added to the red mud (3). The solids areslurried in water (4) and then intensively agitated in a mixer (5) for aperiod of from 1 to about 6 hours at 80 100 C. During this treatment theburnt lime causes causticisation whereby the sodium ions which becomefree are converted by the humic acid into sodium derivatives thereof andare thus maintained in a water soluble form. The solution containing thesodium humates and possible other dissolved ingredients is separated ina suitable apparatus (6) from the water-insoluble remainder of the redmudcoal-calcined limestone mixture. in another apparatus (7) acid (8) isadded to precipitate the humic acids which are recovered with the aid ofa separator (9). The substantially sodium-free solids are fed to a kiln,suitably a rotary kiln (10) where at 700 1,200 C the carbon content ofthe solid remainder brings about a reduction of the iron oxide contentof the red mud. The reduction products are fed into a smelting oven (11)from where the molten iron (12) is recovered by tapping from theremainder which is present in the form of substantially sodium-freeslags (13). These are placed into a cooling container (14). If thestarting composition of the process was properly proportioned, the slagsare mainly constituted of dicalcium silicate which, during cooling, willundergo a, modification through the [3 form to the 'y form whiledisintegrating into small particles. The aluminum content of the powderis leached out with sodium carbonate (15) in a tank (16). The aluminatesolution is separated in a filter (17) and is fed into a precipitator(18) where aluminum hydroxide is precipitated with the aid of CO (19).The hydrate (21) is separated in a filter (20) from the mother liquorwhich is recirculated to the tank (16) to the solid remainder of theleached out powdered slag. The leached out slag remainder is recoveredin a filter (17), can be optionally mixed with additional burnt lime(22) in a homogeniser (23) from where it is fed into a rotary kiln (24)where it serves as a starting material in the manufacture of cementclinker (25).

Alternatively, if the manufacture of higher aluminacontaining refractorycement is desired, then at the outset of processing burnt lime is addedto the red mud in an amount sufficient that the molten slag itself whichis left behind after the molten iron is tapped from the smelting oven(11) is finished, to provide such a refractory cement merely by coolingand grinding.

The present invention is further illustrated by the following examples.

EXAMPLE 1.

An aqueous slurry is prepared from 100 kg (solids basis) red niud, 35.3kg of burnt lime having a 95 percent CaO content, and 25 kg of a 3,500calorie coal, is stirred at 98 C for a period of 3 hours. The startingmaterials had the following composition (in weight percent):

After causticisation, filtration and washing as in Exam 7' ple l, th eremaining solids contained l.O percent Na O based on the dry red mudstarting material.

After the addition of 12 kg coke a reduction of the substantiallysodium-free solids was carried out whereby 26.9 kg iron was recovered.The remaining slag spontaneously disintergrated into a fine powder uponcooling, which was treated as in Example 1. 13.1 kg alumina wasrecovered from the filtrate. The composition of the solid remainder ofthe last filtration was adjusted by mixing it with l0 kg limestone and,after sintering in a tubular oven, 99 kg cement clinker was obtained.

The filtrate of the first step in which the sodium was substantiallyremoved, was treated with a dilute acid, whereupon 1.3 kg pure humicacid was recovered.

We claim:

1. In a method for the processing of red mud wherein the alkali metalconcentration thereof is substantially reduced by contacting the red mudwith burnt lime and wherein the iron content of the red mud is recoveredby reduction of the iron oxides, the improvement comprising contactingthe red mud with humic acid together with the burnt lime, whereby alkalimetal humates are formed and are then separated from the red mud.

2. The water-soluble method of claim 1, wherein the humic acid is addedto the starting material in the form 1 99a! w s Perm t After separationand washing of the remaining solid material it was found to contain 1.2percent Na O, based on the starting red mud solids. 10 kg coke is addedto the substantially sodium-free intermediate product for smelting as aresult of which 27.5 kg iron was recovered. The slag which remainedafter smelting spontaneously disintegrated upon cooling into a finepowder which was treated at 70 C with a 60 g/l Na cO solution. From thefiltrate, after carbonizing and calcination, 11.4 kg A1 0 was recovered.The composition of the solid remainder of the last filtration wasadjusted by mixing it with 20 kg limestone and the mixture was sinteredin a tubular kiln. 8l kg cement clinker was obtained, having a silicatemodulus of 2.2 and an aluminate modulus of 2.0.

The initial filtrate obtained in the removal of the sodium content wastreated with a dilute acid, whereby 1.2 kg humic acid became liberatedand was recovered.

EXAMPLE}.

3. The method of claim 1, wherein from about 1.5 to about 2.5 times thestoichiometric equivalent of the alkali metal content in the red mud, ofburnt lime is employed.

4. The method of claim 3, wherein from about 2 to about 10 times thestoichiometric equivalent of the alkali metal content in the red mud, ofhumic acid equivalent-containing raw material is employed.

5. The method of claim 4, wherein the humic acid or humic acidderivative is added to the starting material in the form of a coal.

6. The method of claim 1, wherein an aqueous slurry of burnt lime, humicacid or humic acid derivativecontaining material, and red mud isagitated at a temperature above ambient and up to C for a period of fromabout 1 hour to about 6 hours.

7. A process for the treatment of red mud, which comprises contacting anaqueous slurry of red mud, burnt lime, and a humic acid -containingingredient, heating the slurry for a period in excess of 1 hour,separating the remaining solids from the solution containing alkalimetal humates, reducing the iron oxides in said remaining solids, andrecovering the iron by smelting.

8. The process of claim 7, further comprising the steps of cooling andgrinding the slag remaining after the smelting, whereby a highalumina-containing refractory cement is obtained.

9. The process of claim 7, further comprising the steps of convertingthe slag remaining after smelting into a spontaneously disintegratingdicalcium silicate, leaching part or all of the aluminum content fromsaid silicate, and converting the remaining solids into portland cement.

2. The water-soluble method of claim 1, wherein the humic acid is addedto the starting material in the form of a coal.
 3. The method of claim1, wherein from about 1.5 to about 2.5 times the stoichiometricequivalent of the alkali metal content in the red mud, of burnt lime isemployed.
 4. The method of claim 3, wherein from about 2 to about 10times the stoichiometric equivalent of the alkali metal content in thered mud, of humic acid equivalent-containing raw material is employed.5. The method of claim 4, wherein the humic acid or humic acidderivative is added to the starting material in the form of a coal. 6.The method of claim 1, wherein an aqueous slurry of burnt lime, humicacid or humic acid derivative-containing material, and red mud isagitated at a temperature above ambient and up to 100* C for a period offrom about 1 hour to about 6 hours.
 7. A process for the treatment ofred mud, which comprises contacting an aqueous slurry of red mud, burntlime, and a humic acid -containing ingredient, heating the slurry for aperiod in excess of 1 hour, separating the remaining solids from thesolution containing alkali metal humates, reducing the iron oxides insaid remaining solids, and recovering the iron by smelting.
 8. Theprocess of claim 7, further comprising the steps of cooling and grindingthe slag remaining after the smelting, whereby a high alumina-containingrefractory cement is obtained.
 9. The process of claim 7, furthercomprising the steps of converting the slag remaining after smeltinginto a spontaneously disintegrating dicalcium silicate, leaching part orall of the aluminum content from said silicate, and converting theremaining solids into portland cement.